Press seal



March 13, 1962 F. J. CAMARATA PRESS SEAL 2 Sheets-Sheet 1 Filed Feb. 18,1960 INV EN TOR.

FIG. 4.

FIG.3.

March 13, 1962 F. J. CAMARATA 3,025,426

PRESS SEAL Filed Feb. 18, 1960 2 Sheets-Sheet 2 United States PatentGfifice 3,025,426 Patented Mar. 13, 1962 3,025,426 PREES SEAL Frank J.Camarata, Upper Montclair, N.J., assignor to Westinghouse ElectricCorporation, East Pittsburgh, Pa., a corporation of Pennsylvania FiledFeb. 18, 1960, Ser. No. 9,638 7 Claims. (Cl. 313-184) This inventionrelates to sealing and, more particularly, to an improved full pressseal for the arc tube of a high-pressure mercury-vapor lamp or the like.

It has heretofore been the practice in the manufacture of are tubes forhigh intensity light sources, such as high-pressure mercury-vapor (HPMV)lamps for example, to attach constricted end sections to a length ofquartz tubing and then collapse them onto the fragile lead-in conductorsconventionally employed in such lamps. More recently there has beendeveloped a socalled full press seal wherein the entire end segment ofthe quartz tubing is collapsed and sealed off thereby eliminating theneed for the aforesaid constricted end sections and proportionatelyreducing the manufacturing cost of the arc tube.

While the adoption of such full press seals permitted the quartz tubingto be made directly into arc tubes without preforming the ends orattaching constricted sections thereto, it also increased the totalamount of heat and pressure required since the entire end segment of therelatively large diametered tube had to be collapsed and molded. This,in turn, required that the sealing fires and press jaws be preciselyadjusted and constantly checked otherwise a prohibitive rate ofshrinkage or poor quality seals would result. In addition, and of equalimportance, the lateral flow of plastic quartz over the fragilelead-inconductors resulting from compressing such a large volume of quartzfrequently placed the conductors under an excessive amount of tensionduring the sealing-in operation causing them to tear thereby ruining theseal and increasing the rate of shrinkage.

It is accordingly the general object of the present invention toovercome and avoid the foregoing and other problems associated with themanufacture of full press seals.

Another and more specific object is the provision of an improved fullpress seal that can be conveniently and quickly formed with a minimumamount of heat and pressure and that will materially reduce thedetrimental forces imparted to the fragile lead-in conductor during thepress-forming operation.

The aforesaid objects, and others which will become apparent as thedescription proceeds, are achieved in accordance with the invention bytightly compressing only the critical portion of the seal assembly, thatis, the portions of the tube end that overlies the lead-in conductor orconductors and that extends laterally therefrom around the bulbousshoulder portion of the tube to the sides of said tube. Thus, only apreselected part rather than the entire end segment of the tube istightly compressed and hermetically sealed. All of the benefits andadvantages of a full press seal are, accordingly, obtained with only afraction of the compressive force and maintenanee heretofore required.

A better understanding of the invention will be obtained by referring tothe accompanying drawings where- FIG. 1 is a fragmentary perspectiveview of a seal assembly comprising an arc tube and a pair ofelectrodeconductor sub-assemblies held in sealing relationship between apair of burner-press jaws preparatory to the press-sealing operation inaccordance with this invention;

FIG. 2 is a perspective view of the full press seal formed on the end ofthe arc tube by the apparatus shown in FIG. 1;

FIGS. 3 and 4 are front views of the work faces of the burner-press jawsshown in FIG. 1;

FIGS. 5 and 6 are front and side elevational views, respectively, of thefull press seal shown in FIG. 2;

FIG. 7 is a cross-sectional view through the finished press seal alongthe line VII-VII of HG. 5, in the direction of the arrows;

FIG. 8 is a cross-sectional view through the finished press seal alongthe line VIIIVlII of FIG. 5, in the direction of the arrows;

FIG. 9 is a cross-sectional view through the seal along the line IXIX ofFIG. 5, in the direction of the arrows;

FIG. 10 is a side view in elevation of an alternative form of theinvention wherein separate press jaws and burners are employed;

FIGS. 11 and 12 are front views of the work faces of an alternative setof press jaws according to the invention; and

FIGS. 13 and 14 are views corresponding to FIG. 7 but show alternativepress seal embodiments formed by the alternative set of press jaws shownin FIGS. 11-12 and another type of press jaw, respectively.

While the present invention may be advantageously employed tohermetically seal any vitreous article of relatively large diameter, itis particularly adapted for use in conjunction with the sealing of HPMVlamp arc tubes and accordingly has been so illustrated and will be sodescribed.

With specific reference to the form of the invention shown in thedrawings, in FIG. 2 there is illustrated one end of an arc tube 15' foran HPMV lamp which tube comprises a light-transmitting envelope ofhighly refractory vitreous material such as a length 16 of quartz tubingof relatively large and substantially uniform diameter, both endswhereof are hermetically closed by a full press seal 18 whichconstitutes part of a flattened end section. As shown, the press seal 18is of generally Y-shaped configuration in that it has a riser segmentthat extends inwardly from the end of the quartz tube 16 centrally andaxially thereof to the bulbous arcuate shoulder 19 of the tube where itbranches into two arm segments that extend laterally around saidshoulder to the sides of the aforesaid flattened end section. Theaforesaid riser segment is of such width that it not only overlies andis hermetically united with a pair of thin and extremely fragile lead-inconductors such as metal ribbons Z0 and 22 but extends therebeyond andincludes the adjoining quartz-to-quar-tz area of the seal assembly aswell. The ribbon conductor 20 is connected at one end to an auxiliaryelectrode 21 sealed inside the quartz tube 16 and at its other end to anexternal terminal lead 25. The ribbon conductor 22, in turn, isconnected at one end to the flattened end of a support rod 23 thatcarries a main electrode 24 and at its opposite end to another terminallead 26. The ends of the aforesaid terminal leads, auxiliary electrodeand support rod are embedded and thus anchored in the axially extendingriser segment of the Y-shaped seal 18.

By virtue of the configuration of the full press seal 18 there isprovided a partly compressed but unsealed and thus raised area 28 ofgenerally U-shaped configuration on the end of the quartz tube 1.6 (seeFIG. 2 and more particularly FIGS. 5-7 and 9). The aforesaid press sealand unsealed raised area together constitute the previously mentionedflattened section at each end of the quartz tube is which section isgreater in width than the diameter of the tube and lies in the sameplane that contains the ribbon conductors 2t) and 22. The raised area 28comprises the flattened but unsealed end and adjoining marginal segmentsof the tube end so that the press seal 18 is located inwardly therefromand is partly surrounded thereby, as shown in FIGS. 2 and 5.

Only one end of the quartz tube 16 is provided with two electrodes 21and 24 as here illustrated, the opposite end having only a mainelectrode as is customary. In order to facilitate locating theconductor-and-electrode assemblies in proper sealing relationship withinthe end of the quartz tube 16 the terminal leads 25 and 26 initially arejoined together by a loop (as shown by the dotted lines in FIGS. 2 andand thus comprise a unitary Ushaped pin. After the press seal 18 hasbeen completed the aforesaid loop is cut off to provide the desiredindividual terminal leads 25 and 26.

In FIG. 1 there is illustrated a preferred apparatus for fabricating theimproved full press seal 18 of this invention. As there shown, the twoconductor-and-electrode assemblies are placed within the end of thequartz tube 16 to provide a seal assembly which is then compressed by apair of press jaws 30 and 32, after the end of the quartz tube 16 isheated and made plastic. The work faces 31 and 33 of the jaws arespecially contoured, as will be hereinafter described, to apply thedifferential sealing pressure required to form the press seal 18. Themain and auxiliary electrodes, together with their respective lead-inand terminal conductor assemblies, are held in proper sealing relationwithin the end of the quartz tube 16 by means of a jig 17 in which thelooped end of the pin connecting the terminal leads 25 and 26 isanchored, the tube in turn being held by a suitable holder 27. As willbe understood, the aforesaid jig, tube holder, and press jaws compriseparts of a Well-known automatic sealing machine that includes means (notshown) for reciprocally moving the jaws toward each other in a directionperpendicular to the plane containing the ribbon conductors 2t? and 22,as indicated by the arrows in FIG. 1.

When the aforementioned seal assembly consisting of the quartz tube 16,the auxiliary electrode 21, the main electrode 24, the support rod 23and their respective lead-in and terminal conductors is indexed intoposition between the press jaws 30 and 32 it is centrally locatedtherebetween as shown in FIG. 1. As shown in the latter figure, and moreparticularly in FIGS. 3 and 4, the work faces 31 and 33 of the aforesaidpress jaws are both of generally semicircular configuration and arecontoured to match one another except for one difference which willhereinafter be described. In this particular embodiment the jaws 30 and32 comprise the heads of gas-burners and their work faces are providedwith a plurality of fine holes 34 that communicate with the interior ofthe respective jaws which, in turn, are connected to a suitable gassupply (not shown), such as a mixture of oxygen and illuminating gas orhydrogen for example. Thus, in this instance the jaws are adapted toapply both heat and differential sealing pressure to the end of thequartz tube 16, the heat being applied in the form of flame jets 35 whenthe work faces of the jaws are not in contact with the quartz.

As shown, each of the semicircular work faces 31 and 33 have a centrallylocated concave cavity or groove 36 that extends radially inward fromthe arcuate edge of the jaw and merges with a much shallower medialgroove or depression 38 that extends from the apex of the groove 36diametrically across to the straight edge of the respective work faces.As shown more particularly in FIGS. 3 and 4, the medial depressions 38are located slightly off center with respect to their respective workfaces and the grooves 36 to enable the rod 23 and main electrode 24 tobe centered as closely as possible within the quartz tube 16 withoutpositioning the auxiliary electrode 21 too close to the inner surface ofthe arcuate bulbous shoulder 19.

Each of the work faces 31 and 33 are also provide 4 with a pair ofelongated marginal depressions 40 that are disposed laterally of themedial depressions 38 and extend parallel thereto from the straightedges of the work faces. The marginal depressions 40, as shown in FIG.1, are deeper than the medial depressions 38 but much shallower than theconcave grooves 36.

The work faces 31 and 33 are identical in every respect except that theone which faces the end of the support rod 23 adjoined to the ribbonconductor 22 (as here shown it is the work face 33 of the jaw 32) isprovided with an auxiliary depression 42 that extends inwardly fromapproximately the apex of the concave groove 36 proximate and parallelto the more centrally located edge of the medial depression 38. Theaforesaid auxiliary depression is dimensioned and located to overlie theflattened end of the support rod 23 that is connected to the ribbonconductor 22 and thus provide a relief cavity therefor.

As shown in FIGS. 1, and 7 and 8, the medial depressions 38 are disposedand dimensioned to overlie and provide relief cavities for the ribbonconductors 20 and 22 whereas the deeper marginal depressions 40 aredisposed and dimensioned to overlie the corresponding marginal orquartz-to-quartz portions of the seal assembly. The length of the medialdepressions 38 is such that the outermost end segment of the tube 16 isnot contacted thereby and is thus flattened but not compressed or sealedduring the press-forming operation. By virtue of the configuration andlocation of the aforesaid grooves and depressions there is provided ineach work face a pair of generally U-shaped lands 44 which, togetherwith the planar recessed surfaces of the medial depressions 38, definethe areas of greatest compression and mold the plastic quartz to formthe generally Y-shaped press seal 18.

The press-forming operation is accomplished by heating the end of thequartz tube 16 until it becomes plastic and then advancing theburner-press jaws 30 and 32 toward each other a predetermined distanceto partially flatten the tube end. The jaws are then returned to theiroriginal open position to allow the flame jets 35 to reheat the quartzand when this has been accomplished the jaws are again advanced untilthe motion thereof is stopped by the pressed quartz.

As shown in FIGS. 7 and 8, when the jaws close the medial depressions 38form a shallow pocket for the ribbon conductors 20 and 22 thereby notonly taking the pressing shock off the ribbons but minimizing thelateral flow of molten quartz in this region during the pressingoperation-both of which serve to prevent tearing of the ribbons. Thepress seal 18 is accordingly slightly thicker in this region by anamount at least equal to and preferably slightly in excess of themaximum ribbon thickness. The marginal depressions it], on the otherhand, form relatively deep cavities for the corresponding portions ofthe tube 16 which are thus merely flattened and left unsealed as shownin. FIG. 7. This latter feature drastically reduces the amount ofpressure required to form the seal insofar as the aforesaid marginalportions of the tube, due to the tube curvature, are not heated to ashigh a temperature as the central portion of the tube and are thus notas plastic and harder to compress.

It should also be noted that while each of the lands 44- are ofgenerally U-shaped configuration only the centrally located portionsthereof actually contact the end of the quartz tube 16 and are used inmolding the seal, as shown in FIGS. 7 and 8. Thus, the effective oroperative areas of the aforesaid lands together with the recessed planarsurfaces of the medial depressions 38 form a pressing surface that isactually of Y-shaped configuration.

As shown in FIGS. 8 and 9, when the jaws are closed the auxiliarydepression 42 in the work face 33 of the jaw 32 overlies and forms apocket for the end of the support rod 23 connected to the ribbonconductor 22. As a result there is provided a reinforcing knot or knob46 of quartz in this critical area that serves to inhibit the formationof cracks in the finished seal as it cools.

As is illustrated in FIG. 1, in order to prevent excessive oxidation ofthe ribbon conductors 20 and 22 during the preheating and press-formingoperations, nitrogen or other suitable inert gas is passed through thequartz tube 16 through a tubulation 48 thereon, the other end of thetube being closed off by a stopper 50 as shown.

As shown in FIG. 10, separate burners 52 may be employed, if desired, toheat the quartz which burners are adapted to angularly direct theirflame jets 53 onto the end of the quartz tube 16 from a location out ofthe line of movement of the press jaws 30a and 3241. In this case thework faces of the aforesaid jaws would only be used for compressing andnot heating the quartz and thus would not have gas openings therein, asillustrated in FIGS. 11 and 12. As there shown, the work faces 31a and33a are identical in every respect to those of the combinationburner-and-press jaws 3t}- and 32 described above except that they aredevoid of the aforesaid gas openings. In addition, it will be noted thatthe medial depressions 38a are partitioned by centrally located andaxially extending rib-like projections 58. The projections 58 are not ashigh as the lands 44a but are of sufficient height to produce and definea region of increased compression in the quartz between the ribbonconductors 20 and 22 when the jaws 30a and 32a are advanced into sealingposition, as shown in FIG. 13. This, in turn, generates lateraloppositely-directed forces in this region during the pressing operationthat forces the ribbons apart and maintains a predetermined spacingtherebetween sufficient to prevent them from shorting out and causing aninternal are that would ruin the arc tube. The resulting indentation ofthe quartz in this area, of course, forms two aligned grooves 60 (FIG.13) that extend axially of the riser segment of the press seal 18a.

As shown in FIG. 14, only a single rib or projection may be provided inone of the jaws to provide a press seal 18b having a riser segment withonly one groove 62 therein. This is suflicient to produce the desiredlateral pressure in the inter-ribbon area and effect the resultantautomatic separation of the ribbons without any possibility whatever ofdangerously weakening the seal.

Experience has shown that the reduction in the criticality of thesealing operation achieved by tightly compressing and closing only thepreselected and necessary portions of the end of the quartz tuberequired to seal-in the ribbons and seal-off the tube in accordance withthis invention has decreased the percent shrinkage due to torn ribbons,leaky seals, etc. by about 80% compared to the previous practice ofcompressing and sealing the entire end segment of the tube.

It will be apparent from the foregoing that the objects of the inventionhave been attained by providing an improved full-press seal wherein onlya preselected part rather than the entire end of the quartz tube iscompressed and sealed off, thereby not only reducing the total amount ofpressure required and rendering the press-forming operation lesscritical but providing a tighter and more durable seal with lessshrinkage.

While several press seal embodiments have been described in detail, itis to be understood that various modifications and refinements thereinmay be made without departing from the spirit and scope of theinvention.

I claim:

1. A vitreous tube having a flattened section at one end that comprisesa sealed portion and an unsealed portion, said sealed portion comprisinga press seal that extends across and hermetically closes off said tubeand constitutes the inward terminus of said flattened end section, andsaid unsealed portion comprising a raised area that merges with saidpress seal and extends a substantial distance along both sides of saidflattened end section from said press seal to the end of said tube.

2. A vitreous tube having a flattened section at one end that comprisesa sealed portion and an unsealed portion, said sealed portion comprisinga press seal that extends across and hermetically closes off said tubeand constitutes the inward terminus of said flattened end section, andsaid unsealed portion comprising a raised area of generally U-shapedconfiguration that merges with and partly surrounds said press seal andconstitutes the tip and adjoining marginal segments of said flattenedend section.

3. A quartz tube of relatively large and substantially uniform diameterhaving a flattened section at one end that is wider than the diameter ofsaid tube and consists of an unsealed portion and a sealed portiondisposed inwardly from said unsealed portion, said sealed portioncomprising a generally Y-shaped press seal the riser segment whereofextends axially toward the proximate end of said tube and the armsegments whereof extend laterally to the sides of said flattened endsection and thereby span and hermetically close off said tube, and saidunsealed portion comprising a raised area of generally U- shapedconfiguration that merges with and partly surrounds said press seal andconstitutes the end and adjoining marginal segments of said flattenedend section.

4. A quartz tube of relatively large and substantially uniform diameterhaving a flattened section at one end that is wider than the diameter ofsaid tube and consists of an unsealed portion and a sealed portiondisposed inwardly from said unsealed portion, said sealed portioncomprising a generally Y-shaped press seal the riser segment whereof iscentrally disposed and extends axially toward the proximate end of saidtube and the arm segments whereof extend laterally to the sides of saidflattened end section and thereby span and hermetically close off saidtube, a metal conductor hermetically embedded in and extending throughthe riser segment of said press seal into said tube, said unsealedportion comprising a raised area of generally U-shaped configurationthat merges with and partly surrounds said press seal and constitutesthe end and adjoining marginal segments of said flattened end section.

5. A quartz tube of relatively large and substantially uniform diameterhaving a flattened section at one end that is wider than the diameter ofsaid tube and consists of an unsealed portion and a sealed portiondisposed inwardly from said unsealed portion, said sealed portioncomprising a generally Y-shaped press seal the riser segment whereof iscentrally disposed and extends axially toward the proximate end of saidtube whereas the arm segments of said press seal extend laterally to thesides of said flattened end section and thereby span and hermeticallyclose off said tube, a lead-in conductor extending through said pressseal into said tube and including a thin metal section that is embeddedin and hermetically united with the riser segment of said Y-shaped pressseal and is joined at its inward end to the end of a metal rod that isanchored in said riser segment and projects therefrom into said tube,the face of said press seal contiguous with the sealed-in end of saidmetal rod being provided with an embossrnent that overlies the end ofsaid rod and reinforces the press seal thereat, said unsealed portioncomprising a raised area of generally U-shaped configuration that mergeswith said press seal and constitutes the end and adjoining marginalsegments of said flattened end section.

6. An arc tube for a high-pressure mercury-vapor lamp comprising aquartz tube of relatively large and substantially uniform diameterhaving a press seal at each end and a pair of spaced lead-in conductorsextending through one of said press seals and connected to a pair ofelectrodes within said tube, each of said press seals being of generallyY-sh-aped configuration with their riser segments centrally disposed andextending axially toward the adjacent end of said tube and their armsegments extending laterally to the sides of said tube and therebyspanning and hermetically closing off said tube at points remote fromthe ends thereof, the marginal and end segments of said tube adjoiningeach of said press seals being flattened but unsealed and constitutingraised areas of partial compression, each of the lead-in conductors insaid one press seal having intermediate metal foil sections that areembedded in and hermetically united with the riser segment thereof, atleast one face of said one press seal having a groove in the risersegment thereof that overlies and is substantially coextensive with thespace between the aforesaid metal foil sections.

7. A vitreous tube that is hermetically closed at a preselected pointalong its axis by a press seal which includes a sealed portion and anunsealed portion, said sealed portion comprising a tightly compressedregion of gen erally Y-shaped configuration the arm segments whereofextend across and hermetically close off said tube, and

said unsealed portion comprising a partly collapsed flattened regionthat is thicker than and merges with said sealed portion and extendsfora substantial distance along both sides of the riser segment of saidY-shaped sealed portion.

References Cited in the file of this patent UNITED STATES PATENTS2,664,517 Wiener Dec. 29, 1953 2,675,496 Unglert et a1 Apr. 13, 19542,816,398 Pearson Dec. 17, 1957 2,848,641 Peterson Aug. 19, 19582,857,712 Yoder et al Oct. 28, 1958 2,876,377 Retzer et al Mar. 3, 19592,884,743 Hunter May 5, 1959

